Catalyst for reducing ammonia emissions

Abstract

The present invention relates to a composition comprising platinum supported on titanium oxide, the platinum particles having an average particle diameter of 50-200 nm. The composition has a surprisingly low light-off temperature for the ammonia oxidation and a high selectivity for oxidation to N2.

The invention claimed is: 
     
         1 . Composition comprising platinum in the form of platinum particles supported on metal oxide A, characterized in that the platinum particles have an average particle diameter of 50-200 nm, wherein metal oxide A is titanium oxide. 
     
     
         2 . Composition according to  claim 1 , characterized in that the platinum particles have an average particle diameter of 80-120 nm. 
     
     
         3 . Composition according to  claim 1 , characterized in that the composition contains no further precious metal other than platinum. 
     
     
         4 . Composition according to  claim 1 , characterized in that the titanium oxide comprises the crystalline phases anatase and rutile, and the anatase to rutile ratio is greater than 9:1. 
     
     
         5 . Composition according to  claim 1 , characterized in that the platinum loading is 0.5-20% by weight based on the metal oxide A. 
     
     
         6 . Composition according to  claim 1 , characterized in that the platinum loading is 3-8% by weight based on the metal oxide A. 
     
     
         7 . Composition according to  claim 1 , characterized in that the metal oxide A contains silicon oxide, wherein the proportion of silicon oxide in the metal oxide A is 1 to 10% by weight. 
     
     
         8 . Composition, characterized in that it comprises a composition according to  claim 1  and metal oxide B, wherein metal oxide B equals metal oxide A. 
     
     
         9 . Method for producing a composition according to  claim 1 , characterized in that the platinum is deposited from a solution on the metal oxide A and the composition is subjected to a thermal treatment at 700° C. to 900° C. after drying. 
     
     
         10 . Catalyst comprising a composition according to  claim 1 , characterized in that the composition is applied to a carrier substrate of length L. 
     
     
         11 . Catalyst according to  claim 10 , characterized in that the composition is applied to a carrier substrate over at least 80% of the entire length L. 
     
     
         12 . Catalyst according to  claim 10 , characterized in that the composition is applied to a carrier substrate over a length of 10% to 80% of the carrier substrate length L. 
     
     
         13 . Catalyst according to  claim 10 , characterized in that the composition is applied to a carrier substrate together with another catalytically active composition that is active for SCR reaction. 
     
     
         14 . Catalyst according to  claim 10 , characterized in that the composition and another catalytically active composition are arranged in different zones and/or layers. 
     
     
         15 . Catalyst according to  claim 10 , characterized in that the carrier substrate is a ceramic or metallic substrate. 
     
     
         16 . Catalyst according to  claim 10 , characterized in that the carrier substrate is a flowthrough substrate. 
     
     
         17 . Catalyst according to  claim 16 , characterized in that the flowthrough substrate is a corrugated substrate. 
     
     
         18 . Catalyst according to  claim 10 , characterized in that the carrier substrate is a filter substrate. 
     
     
         19 . Catalyst system, characterized in that it comprises a catalyst according to the invention in accordance with  claim 10 . 
     
     
         20 . Method for reducing nitrogen oxides in exhaust gases of lean-burn internal combustion engines, wherein the exhaust gas is passed over an exhaust gas system that comprises a catalyst for the selective reduction of nitrogen oxides (SCR) and an ammonia slip catalyst (ASC) downstream of the exhaust gas stream, characterized in that the ASC is a catalyst according to the invention in accordance with  claim 10 . 
     
     
         21 . Method according to  claim 20 , characterized in that the SCR catalyst is a vanadium oxide-based catalyst or a zeolite-based catalyst of the Fe-zeolite or Cu-zeolite type.